1. Field of the Invention
The present invention relates to a bookbinding apparatus for binding recording sheets having images formed thereon by an image forming apparatus and discharged therefrom, into a book, the image forming apparatus, and a control method.
2. Description of the Related Art
Conventionally, an image forming system has come into wide use which is comprised of an image forming apparatus and a post-processing unit, and is configured to be capable of performing image forming processing and subsequent post processing on recording sheets. In an image forming system of this type, images are formed on recording sheets based on digital image data, and then the recording sheets are conveyed into a post-processing unit, followed by being subjected to post processing (stapling, punching, folding, etc.) online.
Further, in recent years, there has come on the market an image forming system having an image forming apparatus connected to a case binding machine that performs case binding by applying glue to one side of a recording sheet bundle as a main body of printed matter, bonding a cover sheet to the glue-applied side of the recording sheet bundle, and then cutting the other three sides of the recording sheet bundle covered by the cover sheet.
In a case where a case binding operation is performed by a case binding machine, a recording sheet bundle is shifted within the machine in accordance with the progress of the operation. The case binding machine includes a processing section having a complicated mechanism for applying glue to a recording sheet bundle, cutting the same and so forth, and hence even after the power of the machine is turned off, it is difficult for an operator to put his/her hand into the processing section. This makes it impossible for the operator to handle the recording sheet bundle until it is discharged as a product after going through the case binding process.
To eliminate this inconvenience, there has been proposed a method of discharging a recording sheet bundle from a case binding machine (see e.g. US Patent Publication No. 2007/0085256). In the method disclosed in US Patent Publication No. 2007/0085256, when preparation of a cover sheet fails before a step of sticking the cover sheet to a recording sheet bundle, a cancellation process is executed in which only processing for applying glue to the side of a recording sheet bundle is performed without sticking the cover sheet to the recording sheet bundle and then the recording sheet bundle is discharged after drying the glue.
On the other hand, there has been proposed a method of processing to be executed when the power of a case binding machine is turned on again after turn-off of the power (see e.g. Japanese Patent Laid-Open Publication No. 2007-44821). In the method disclosed in Japanese Patent Laid-Open Publication No. 2007-44821, information on the progress of cutting processing in a step of cutting a recording sheet bundle is stored in a memory, and when the power of the case binding machine is turned on again after turn-off of the power due to a power failure or for troubleshooting a sheet jam or the like, the continuation of the cutting step is carried out based on the information on the progress of the cutting processing stored in the memory.
A conventional case binding machine of the above-mentioned type suffers from the following problems: When the power of the case binding machine is turned off due to occurrence of a trouble immediately before glue is applied to a recording sheet bundle, the recording sheet bundle which is to be glued remains in the machine. In the meantime, heated glue prepared for the recording sheet bundle is cooled. For this reason, when the power of the case binding machine is turned on, preparation for glue application is restarted so as to apply glue to the recording sheet bundle remaining in the machine and then discharge the same.
In this case, the recording sheet bundle remaining in the machine has no cover sheet stuck thereto, and hence the recording sheet bundle cannot be a product. Therefore, the recording sheet bundle remaining in the machine is discharged as a defective product, and it is a waste of time to execute the same preparation for a glue application as in the case of a normal binding operation for a recording sheet bundle discharged as a product. Further, depending on the arrangement of a case binding machine, it is sometimes impossible to convey recording sheets from the image forming apparatus to a post-processing apparatus other than the case binding machine until the gluing of the recording sheet bundle is completed. In such a case, not only the case binding operation but also operations for the other post processing cannot be executed.